Optical filters are widely used to control visible and solar energy. Most notably, optical filters have been used as glazings in window technology (e.g. windows of buildings, vehicles, aircraft, spacecraft, ships or the lie) to control the flow of light and heat into and out of the glazing, for glare reduction and energy load management. Improving the energy efficiency of buildings is a key aspect of reducing energy use and reducing CO2 emissions. Buildings consume about 39% of all energy and 68% of the electricity used in the United States, and are responsible for about 38% of all greenhouse gas (GHG) emissions. Windows are responsible for about 30% of a building's energy loss. As such, windows with improved technology for reducing heat loss and solar heat gain can offer significant benefits and cost savings.
Optical filters (“tinted windows”) may be used in vehicle windows to provide privacy for occupants, prevent glare and/or reduce solar heat gain without sacrificing visibility. Static tints generally cannot be altered, and if further ‘darkening’ is desired, a blind may be drawn—eliminating any visibility for the occupants. ‘Panoramic’ sunroofs may be installed to provide visibility to occupants (e.g. for sightseeing—‘dome roofs’) and provide a feeling of ‘being outside’, a drawn blind does not accommodate this desire, and for a large roof or dome, may be difficult for a user to manipulate at will.
Optical filters have also found application in ophthalmic devices to control the light impacting the eye. Applications include, for example, prescription and nonprescription glasses, goggles, sunglasses, visors, and safety eyewear.
There are a number of technologies that have been used in optical filter applications for dynamically varying the degree of visible light transmittance, including photochromics, electrochromics, liquid crystals, thermochromics, and suspended particle displays.
Some optical filters used in window applications requiring the application of electrical voltage to vary the degree of visible light transmittance—such devices typically comprise two transparent conductive electrodes on opposing substrates to which the electrical voltage is applied. These transparent conductive electrodes can be formed using a conductive coating such as indium-tin oxide (ITO) on glass or polymeric film. A material that transitions from one state of visible light transmittance to another upon the application of electrical voltage is sandwiched between the two transparent conductive electrodes. For example, electrochromic technology involves applying thin coatings of electrochromic materials to two transparent conductive electrodes and sandwiching an electrolyte material in between. Electrochromic technology typically requires the user to apply external electrical power to darken. Electrochromic technology is used in auto-dimming automobile mirrors (for example, those made by Gentex Corporation of Zeeland Mo.).
Another example of electrochromics is in window applications (Sage Electrochromics Inc. of Faribault, Minn.) that incorporate thin coatings applied to one of the glass layers in a window. Application of electricity with the positive lead connected to one electrode causes the window to darken, and application of electricity with the positive lead connected to the other electrode causes the window to lighten. The electrochromic coating that is applied to the glass involves the use of specialized coating processes such as sputtering and chemical vapor deposition. This often requires a specialized factory or facility requiring the glass to be shipped to one central factory for the coating process to be performed, and then shipped out to wherever they will be used. As such, windows made using electrochromic technology can be quite expensive. This type of window system also employs an electrode system with two conductive transparent electrodes on opposing substrates.
Electrochromics have also been used in ophthalmic devices. For example, ChromoGenics of Uppsala, Sweden makes an “electrochromic foil” for use in motorcycle helmet visors and other products by making a multi-layer electrochromic device between two plastic films. Relatively low DC voltages are used for switching the electrochromics from one state to another but power is typically required to maintain the electrochromic device in the dark state. These electrochromic foils also utilize an electrode system with two conductive transparent electrodes on opposing substrates.
Patterning of ITO (indium tin oxide) has been used to prepare for liquid crystal displays and touch panels. The objective of patterning the ITO in these cases is to create an array of pixels such that each pixel can be uniquely addressed and either turned on or off or a touch detected, depending on the application.
Interdigitated electrodes have been described in the design of organic electrochromic devices with three-electrode dynamic operation for display technology (Galit Bar et al., “A new approach for design of organic electrochromic devices with interdigitated electrode structure,” Solar Energy Materials & Solar Cells (2009) 93:2118-2124)).
U.S. Pat. No. 7,323,634 describes a method of forming an electronic circuit component using the technique of drop on demand printing to deposit droplets of deposition material, the method comprising depositing a plurality of droplets on a surface to form a patterned electronic device comprising multiple discrete portions.
United States Patent Publication No. 20070128905 describes transparent electrical conductors comprising regions of high transparency and regions of lower transparency, but higher conductivity. This allows electrical connection through the conductor, while retaining its transparency for such applications as hand-held device display screens or transparent antennas, for example.
United States Patent Publication No. 20070153355 describes an electrochromic film and demonstrates the electrochromic effect of a single substrate film by applying electronic current to induce a reversible oxidation-reduction reaction of an organic electrochromic layer. The electrochromic film can attach to a surface of an object with the use of an adhesive layer.
U.S. Pat. Nos. 6,597,489 and 6,606,184 describe an electrode device for an electrochromic device, where the electrodes are disposed on a substrate in a substantially coplanar relation. An electrochromic medium comprising a cathodic and an anodic species, at a ratio within the electrochromic medium in relation to the surface areas of the positive and negative electrodes is described.